There is a more and more widely use of Memory, such as OTP, in integrated circuit to control various circuit parameters. Circuits used one wire programmable interface can be found in programmable amplifier, programmable clock, programmable potentiometer, programmable capacitor, programmable SOC, programmable integrated sensor as well as ASIC used in the sensor calibration and temperature compensation.
SPI (4 wire) and I2C (2 wire) protocol has the advantages of fast communication as well as high reliability, they are widely used in communicating with the internal memory from the outside circuit, but they required extra circuit terminals (4 wires and 3 wires)
One wire programmable or single wire programmable protocol only adopts one terminal (one wire) by using the same circuit terminal as both the circuit output terminal and the digital I/O terminal the circuit uses to interface with external circuit. The protocol therefore doesn't need extra pin to digital interface with external circuit. Using the protocol, one wire programmable circuit can be pin to pin compatible with their non-programmable counterparts, and programmable circuit that requires only three pins, VDD, GND and Output can be realized. The one wire programming protocol is widely used in circuit designed for sensor calibration, programmable amplifier, programmable clock, programmable potentiometer, programmable capacitor, programmable SOC etc.
The one wire programming protocols in prior arts were realized by monitoring the status of one wire terminal (OUT) when the circuit is powered up. If during powered up, in at predetermined time slot, the one wire terminal (OUT) receives predetermined signals, then, the circuit goes into interfacing mode, of which external interface circuit can Read (i.e download data from one wire programmable circuit, or Write, i.e. upload data to the one wire programmable circuit or Program, i.e. fusing the OTP by passing high current through the OTP in the one wire programmable circuit). If during the predetermined time slot, no predetermined signals are received, the circuit goes into its normal output mode. The circuit will not change its operation mode until it is shutdown and powered up again to decide which state to go into. Since switching between the interfacing mode and the normal output mode would require the circuit to be shutdown and then powered up, the process prolongs the time needed to find the right OTP code as well as programming the OTP due to the fact that many times of switching between the interfacing mode and the normal output mode are required in the process to find the right OTP code. The requirement of switching between the interfacing mode and the normal output mode also makes the test system complicated.